Weather Outlook: More rain in September; mild winter? | Michigan Farm News
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Weather Outlook: More rain in September; mild winter?

2018-09-15 181 Jeff Andresen | MSU Extension

A broad upper-air ridge across the Upper Midwest led to a very active weather pattern across Michigan and the Great Lakes region during the last week of August and first week of September, with significant rainfall across most areas of the state.

Almost daily rounds of showers and thunderstorms during this period brought very heavy rains (in some areas more than six inches) to much of central Lower Michigan. In general, the rains reduced or ended abnormally dry conditions in many areas.

The active weather pattern also resulted in at least nine confirmed tornado touchdowns (an unusually high number for late summer) and a variety of high-wind damage across the state between the 28th of August and 3rd of September.

Rainfall totals for August varied widely across the state, ranging from more than 10 inches (and 200-300 percent of normal totals) at a few spots in the central Lower Peninsula to less than 2 inches across far southeastern sections of the state.

Prior to the late-month wet weather, drought conditions intensified across many sections of the state, including the northern Lower Peninsula, where the U.S. Drought Monitor upgraded conditions to ‘D2’ or Severe Drought. It was the first appearance of D2 conditions in Michigan since the drought of 2012.

By month’s end, 60 percent of the state was still considered abnormally dry, with 24 percent remaining in Moderate or Severe Drought categories, down slightly from the peak in mid-August (these percentages are expected to decline further in the short term given the recent rainfall).

Mean temperatures for August were generally warmer-than-normal statewide, ranging from close-to-normal across the western Upper Peninsula to more than 4 degrees F above normal across sections of Lower and eastern Upper Michigan. Base 50-degree growing degree-day totals from the beginning of May through the end of August ranged from less than 1800 units across central sections of the Upper Peninsula to almost 2600 units along the Indiana and Ohio border (generally from about 100 to more than 300 units above normal).

Most medium-range guidance suggests at least a short-term continuation of the western troughing/eastern ridging upper air pattern described above that would result in additional warmer and wetter-than-normal weather.

One forecast challenge will be the possibility of additional rainfall from the remnants of land-falling Atlantic Basin hurricanes and tropical storms, given the forecast jet stream pattern and that the tropical Atlantic became very active during late August. Such events are not common in Michigan, but occasionally bring significant rainfall to the state.

As a result, the modified version of the Climate Prediction Center issued at the end of August now calls for increased odds of above-normal precipitation totals for the month as a whole (it had earlier called for the Equal Chances, no forecast direction for precipitation totals).

It is important to note that there are also some hints of drier weather further ahead (late September) which would favor maturation and field dry-down of most crops and allow wet soils to dry/drain.

For forecast temperatures, virtually all long-lead outlooks call for warmer-than-normal mean temperatures through the fall and likely into the upcoming winter season.

The longer-lead outlooks are heavily based on the expected development of El Nino conditions in the tropical Pacific region later this fall and winter.

Climatologically, El Nino conditions are linked with milder and drier- than-normal winter weather across the Upper Midwest, especially during the middle and latter portions of the season. 

Andresen is a professor of Meteorology/Climatology with Michigan State University’s Dept. of Geography, Environment, and Spatial Sciences; MSUE specialist and the state climatologist for Michigan.  

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